Can The Flu Shot Cause The Flu?

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Photo by Diego Cupolo via Flickr. Creative Commons License
Photo by Diego Cupolo via Flickr. Creative Commons License

Jenny T. Asks:  I’d love to see a detailed discussion on why the flu vaccine can not possibly cause the flu. This is the number one excuse I hear over and over again.

Our Answer: Hi Jenny, that is indeed a concern we’ve heard and it’s one that we think we can address pretty well. It helps to know how flu vaccines are made. The injectable flu vaccines (shots) are all either inactivated (killed) viruses or recombinant (only fragments of a virus, not whole viruses). So there is absolutely no chance of them causing flu illness because they aren’t live and cannot replicate. Continued

Are Vaccines Safe With Egg Allergies?

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Laura S. Asks:
Hi, can you educate me about the use of eggs to make vaccines? I’m pro vaccine but my son has an egg allergy and I just want to understand it better. Thanks!

Our Answer:
Hi Laura, thank you for your question! Luckily, most vaccines are completely egg free and should not pose a problem for your son at all. There are a couple, however, that may contain small quantities of egg and you should speak with your doctor and allergist before proceeding with them. In the US, the main one you’ll need to talk to your doctor about is the influenza vaccine; according to the CDC, most versions of the influenza vaccine contain small quantities of egg (there is an influenza vaccine free of egg protein, but it’s only approved for people over 18). Because the quantities of egg protein in the vaccine is very low, it can usually still often be given to people with egg allergies, depending on the severity of the allergy. The best thing to do is consult with your doctor about your child’s specific health needs, but it is likely that he’ll be able to receive the vaccine. If your doctor approves, you should definitely remain in the doctor’s office for 30 minutes after receiving the vaccine, just for monitoring purposes.

Additionally, the vaccines for yellow fever, tick borne encephalitis, and one version of the rabies vaccine may contain small quantities of egg, but these vaccines are not typically given in the US. We should also note that the MMR vaccine is grown in chick embryo tissue culture, but several studies have documented the safety of MMR in children with egg allergy and as such, egg allergy is not a contraindication to the MMR vaccine.

We hope this helps!

Additional Reading:

Egg allergy safety data from the Public Health Agency of Canada:

Precautions and Contraindications for vaccines from the Immunization Action Coalition:

Photo Credit to Kate Ter Haar. Creative Commons license.

Understanding Vaccine-Derived Polio

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Administration of an oral polio vaccine to a young child
Photo Credit to the RIBI Image Library, Creative Commons License.

A rare, mutated form of poliovirus has caused paralysis in 2 children in the Ukraine. Several articles discuss what happened but it’s important to also understand the implications.

First, the polio vaccine currently used in the US and most developed
countries is the inactivated polio vaccine (IPV); the use of oral polio vaccine (OPV) was discontinued in the US in 2000. It is not possible for IPV to cause paralytic poliomyelitis (the debilitating disease caused by poliovirus). It is not possible for IPV to shed and infect another person. It is not possible for IPV to mutate into a disease-causing virus strain. OPV, on the other hand, while highly effective in producing immunity to poliovirus, is a live, weakened poliovirus (actually a combo of 3 poliovirus strains, but that is neither here nor there) that can, in rare cases (1 in every 2.7 million first doses), cause vaccine-associated paralytic polio in a recipient (thought to be triggered by immune deficiency), and also very rarely and over time, mutate into a disease-causing virus similar to wild-type poliovirus.

In the recent cases of polio in the Ukraine, while it is true that the strain of poliovirus that caused disease was a mutated form of the OPV strain, it is also true that the cases of polio disease would not have occurred if there was a high enough vaccination rate in the community. Poliovirus is an RNA virus, and RNA is highly prone to errors while replicating, thus causing mutation. As a comparison, when DNA is replicated, there is an error about 1 per billion nucleotides, whereas RNA replication makes a mistake in about 1 per 10,000. This actually corresponds to an average of 1 mutation per whole poliovirus that is replicated. Mutations are random, so sometimes a mutation will change nothing in how the virus acts, sometimes it will make the virus stronger, sometimes it will make the virus weaker. However, the more chances that a virus gets to replicate, the more chances it gets to “win” in the evolutionary game… it will have more of a chance to hit that set of mutations to make it replicate faster and cause disease.

Let’s travel the route of an OPV virus in 2 populations. The first is a community such as the Ukraine, where the vaccination rate is a low 50%. A person receives OPV, the vaccine strain virus replicates slowly in the gut over several weeks while the person produces an immune response, which will then eliminate the vaccine strain virus well before it can do any harm. However, during this time, the vaccine recipient perhaps did not do a great job washing hands after using the bathroom and spreads the vaccine strain virus to 10 people close to them, 5 of whom are unvaccinated. This is actually not a bad thing as now these 5 unvaccinated people receive “passive” immunization and they now produce antibodies to poliovirus, although the vaccine strain virus also slowly replicates in their gut while the person mounts an immune response… which then spreads to other unvaccinated people in close contact, and so on. This can occur silently over many years. However, all this time, the vaccine virus is getting a chance to replicate further, which means more chances of hitting the lottery and mutating into a form that can cause harm just like wild-type poliovirus. Another way to look at it is like playing the game telephone, where you have a long line of kids and one person whispers something to the first person, who then whispers it to the next person, and so on. The longer the message goes down the line, the more chances for the message to get distorted.

Now, let’s travel the route of OPV in a population with a high vaccination rate. In this case, a person receives OPV, the vaccine strain virus replicates slowly in the gut, and even though this person exercised poor hygiene, all the close contacts around the person have been vaccinated, so when they are exposed to the vaccine strain virus, their vaccine-primed immune systems attack the virus before it gets a chance to replicate and be further spread. So in this scenario, rather than allowing a message to get distorted along the way by playing telephone, it’s like everyone got the message first-hand, from the source, so it’s in the original form.

The U.S. and other developed countries can rest easy that it isn’t possible for IPV to mutate into a disease-causing form. However, poliovirus, whether wild-type or OPV-derived, is only a plane ride away, which means it is very important that we continue to vaccinate here in the U.S. In addition, there have been rare cases of long-term shedding of live poliovirus in immune deficient recipients of OPV, and since OPV was still in use up to year 2000, the possibility still exists for exposure to vaccine-derived poliovirus within the U.S. The elimination of wild-type poliovirus from the U.S. has led to a false sense of security where there are now community pockets with low vaccination rates against polio. And since IPV doesn’t have the “passive” immunization benefits of OPV, only those who are vaccinated are protected if exposed to disease-causing poliovirus. Continued

Injection VS Ingestion

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Anonymous Asks:
A related question about the aluminum that I haven’t seen addressed — All of the examples of amounts in daily life include casual exposures or ingestion — not injection. Is there a difference in how the body might respond to injected aluminum, versus aluminum passing through the gut?

Our Answer:
Thanks for this question — it’s a good one, and a complicated one to answer! Sorry it took us some time to get back to you. Generally speaking, the answer is yes and no — how the body processes/responds to something depends a lot on how much gets into the bloodstream, because once it’s there, it will be handled the same, regardless of where it started out. Depending on the route of administration (like injection versus ingestion) the amount that makes it to the bloodstream can differ.

First, some basics about aluminum and aluminum in vaccines (which you may already know). Aluminum is a very abundant element, and is found in soil, plants, some foods, water, cows milk, breast milk, baby formula, etc. Not all vaccines contain aluminum, but the ones that do, contain aluminum not in the heavy metal form, but in the form of a salt, like aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate (which is called alum). These components, called adjuvants, are added to a vaccine to stimulate a stronger immune response; they can help ‘recruit’ immune cells to the site of injection and make the vaccine more effective. They’ve been used safely in vaccines for more than 60 years.

It’s important to note that aluminum salts are not ‘bioavailable’ – which means that they cannot be taken up directly by cells. Or in other words, there’s no point in keeping it around, because our body cannot make use of it, and so it gets excreted (more on that in a moment). While we are being exposed to and consuming aluminum constantly throughout our life, the vast majority of that aluminum is ingested, digested and then excreted by the kidneys. Very little is maintained in the body. But you’re right — the aluminum in vaccines is injected, not ingested. Does this matter? Well, not all of the aluminum contained in vaccines makes it into our bloodstream right away, but most of it does. Once there, the aluminum gets bound to carrier proteins, taken to the kidneys, and excreted. Only a very tiny amount is retained in the tissues of the body. This amount will decrease over time. Is this problematic? Well, this is where the bioavailable part comes in. The aluminum that may remain in the muscle tissue isn’t absorbed by cells, and researchers don’t have any evidence to suggest that there’s any risk that the quantity or the duration of the aluminum could be harmful.

Speaking of research, there has been a lot of research on this topic, as parents have expressed concern over aluminum adjuvants, and the medical and public health communities are always doing their best to make sure the vaccines we use are as safe and as effective as possible. A large review conducted in 2011 studied this particular issue very carefully. They wanted to know if the amount of aluminum infants are exposed to in the current immunization schedule could be problematic once added on top of the aluminum present at birth and acquired through breastfeeding/formula, food and the environment. They used the best methods currently available to measure how aluminum is absorbed, processed and secreted, the timing of immunizations in the recommended schedule, and the known amount of aluminum in vaccines. They found that the amount infants are exposed to is well below the lower limit of what they think could be harmful, even for low birth weight babies.

It’s important to say that there is such as thing as aluminum toxicosis in humans, but it happens exclusively in people with severe kidney disease who are being given intravenous medicines with very high aluminum content, or in those exposed to extremely high levels of aluminum via their occupation. The amount in vaccines and food doesn’t come anywhere close to that.

So — what does this mean for your question? There is truth to the idea that compounds ingested vs. those that are injected might be handled differently by the body, and in some ways, this is true for aluminum in vaccines. However, what matters is this: 1) the vast majority of aluminum in vaccines makes it to the bloodstream quickly and is excreted within hours; 2)What amount may remain in tissues will also be processed and excreted within days, but we don’t have evidence to support that this is harmful; 3) The amount of cumulative aluminum exposure (food+ environment + vaccines) does not cross the threshold of what we know to be dangerous, even for the smallest infants. Hopefully this is helpful!

Photo Credit to Sami Keinänen. Creative Commons license.

Vaccine Safety and Retracted Studies

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Sara K. Asks: With the recent news (npr) shows discussing issues in the peer-review process, please tell me why vaccine safety isn’t in question. Thx!

Our Answer: Hi Sara, thanks for the question! I assume you’re referring to the recent coverage of the study on attitudes regarding gay marriage that was retracted? It’s valuable that attention is being given to the peer-review process and better understanding why scientific data must be examined rigorously. It’s an important thing for everyone to understand better.

Yes, a certain number of peer-reviewed studies are retracted every year and there are certainly some additional number of studies that are faulty in some way but are overlooked and not retracted. It’s something to be aware of, absolutely, although a .02% (give or take) failure rate isn’t sufficient for us to say we should simply throw out the process of peer review. It’s also worth noting that retraction is a normal part of the peer review process, peer review happens both before a study is published, and continuously as published studies are examined by other scientists.

So, why isn’t vaccine safety in question? There’s a critically important difference between this recent study and the studies proving vaccines to be safe. That difference is replication. The problems with the falsified data in the study currently under discussion came to light very rapidly when another group of researchers pursued replicating the results. If your science isn’t valid, either because you falsified data or because you committed some critical error in testing, it won’t be possible for another researcher to replicate your results. In the case of vaccine safety studies these results have been replicated again and again, in different conditions, by different research teams, and they have produced the same or very similar results. Even still, we continue to research and review the safety of vaccines to verify that nothing has been missed. Science isn’t a set of carved in stone facts, it’s a continuous process. All the best scientific evidence so far – and there is a great deal – shows that vaccines have a very high level of safety, but the nature of the scientific process is such that we won’t simply accept that as gospel, but will continue to verify and investigate what we know about vaccination and the human immune system.

This doesn’t mean that there are never mistakes. It’s absolutely critical that the scientific community continue to investigate vaccine safety with a critical eye, and that is exactly what is done.

Conversely, we often see people bringing forth a study they’ve seen somewhere that appears to prove some hidden danger of vaccination. In most cases, these studies have faulty methods, and/or cannot be adequately replicated (as was the case with Andrew Wakefield’s famously discredited work). On balance, when we examine the body of scientific research on vaccination (which is no mean feat, by the way, and the reason we have and need highly educated scientists on our admin staff) we see that the studies which can be validated and replicated overwhelmingly point to a high degree of safety for vaccines. The scientific process isn’t perfect, but it is very, very, good, and it’s the only rigorous and objective method we have for examining vaccine safety.

I hope this helps shed light on the difference between individual retracted studies and the overall body of research on the subject of vaccination. Thank you for messaging us!

*** As always, if you have a question you would like to see addressed on the the page or privately via PM, feel free to send us a message. ***

Photo Credit to U.S. Army RDECOM. Creative Commons license.

Q&A: MMR & MMRV Safety

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Anonymous Asks: I’ve heard there is a new version of the MMR shot that includes the chickenpox vaccine too. My son will be getting his one year shots soon, and I’d like to know if the new version is safe.

Our Answer: Thanks for your question! Yes, there are now two options for children age 12 months to 12 years when it comes to protecting them from measles, mumps, rubella and varicella: Using the combination MMR vaccine plus the stand alone varicella vaccine in two separate injections, or a combination that contains all four, called MMRV.

Children need to receive two doses of vaccine to protect them against these four diseases.

The first is recommended at age 12­15 months, the second is recommended at ages 4­6 years. The recommendations differ for the first and second dose, based on what we know about the side effects. For the first dose, in the child’s second year of life (age 12­24 months) either option can be given, however, the CDC recommends using MMR and varicella separately, rather than the combination MMRV vaccine. Giving MMRV together requires one less injection, but there are data that suggest that MMRV when given for the first dose (between ages 12-­23 months) is associated with a slightly higher risk of fever (102 or higher) within 42 days after the vaccine is given, especially within 5­12 days, as well as a slightly higher risk of febrile seizures during that time compared to those who get the separate MMR and varicella vaccines at the same visit.

Studies show that the MMRV combination is associated with fever in about 22 out of every 100 children vaccinated, versus about 15 out of every 100 children vaccinated when the separate MMR + varicella vaccines are used. Likewise for febrile seizure, MMRV is associated with febrile seizure in about 8 out of every 10,000 children vaccinated vs. 4 out of 10,000 children vaccinated when MMR + varicella are used.

Febrile seizures are seizures caused by a high fever. 2­5% of children under 5 years will have at least one, and they are most common in 14­18 month olds. As MMR and varicella are live attenuated vaccines, it is not uncommon for the child’s immune system to mount a fever as it responds to the vaccine (which is a good thing actually, it means the vaccine is doing it’s job of ‘tricking’ the immune system into thinking it’s the real virus and therefore is creating protective antibodies). It is believed that febrile seizures occur in young children because the brain is still learning how to cope with fever.

It’s important to note that while febrile seizures can be extremely distressing for parents, they are usually not associated with any long term complications. Children should be evaluated by a physician, but invasive testing and medication are not usually required, unless a more serious underlying condition, like epilepsy, is suspected or found. Febrile seizures can run in families. If your child has a family history of febrile seizures, be sure to discuss this with your pediatrician.

For children ages 4­6, the data do not suggest an increased risk of fever or febrile seizures with MMRV vaccine compared to those receiving MMR and varicella separately (whether for the first or second dose). Therefore there is no basis for a scientific or medical preference for MMR and varicella separately vs. MMRV combination in this age group. However, the combination MMRV requires one less injection, and so may be preferable to parents (or their toddlers!).

Further Reading:

Red Wine & Applesauce on MMR versus MMRV side effects.

CDC info on MMRV:

Q&A on MMR and MMRV from the CDC.

Pediatrician’s Fact Sheet on MMR and MMRV from the CDC.


Photo credit to njxw. Creative Commons license.

Q&A – What’s The Story With Non-Injected Vaccines?

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Vaccination-polio-indiaAlissa R. Asks: Hi! I had a question which I’m not sure has been addressed. What’s the likelihood of developing some other way of administering vaccines?  I keep hearing things about different methods and want to know how much truth there is in it and how close they are to developing another way if any?

Our Answer: That’s a great question! There are a number of methods being explored to create vaccines that are administered some other way besides injection. The challenges with these methods are to create an adequate immune response that is at *least* as good, or better, than what already exists. Briefly, injected vaccines work by recruiting immune cells to the site of the injection: it gets injected into the muscle, and the subsequent inflammation attracts the attention of immune cells, which then ramp up production of specialized cells to fight the particular pathogen the vaccine is designed to protect against. One of the reasons some vaccines contain alum (an adjuvant made with aluminum) is actually to increase the local inflammation to recruit more immune cells. (Think of the alum as the class bully saying, “Yo! Immune cells! You think you’re all that? Well, come and get a piece of this!”)

That’s one of the reasons injected vaccines are so effective and ingested vaccines are so rare. When you ingest the vaccine, the stomach acids can make short work of it before it has time to induce an inflammatory response. (The exceptions are the polio vaccine and rotavirus, who can hack it in the digestive system.) So, to develop additional vaccines that aren’t injected, they need to invoke the same local response. The aerosol flu vaccine does this well because we actually catch flu through the respiratory tract. Creating an immune response in the nose, at the site where we’d normally catch the disease, makes sense. Measles, another respiratory infection, can also have an aerosol-delivered vaccine, and in fact one has been used in Mexico for a number of years. The problem is that it’s not as effective as the injected one. (One of our admins recently wrote about a new study on the aerosol measles vaccine. Notice there that Dr. Poland points out the researchers didn’t measure the local response, which he thinks might have shown a stronger immune response. Both the local and the overall response are helpful to a vaccine’s effectiveness.)

Meanwhile, researchers are continuing to get better at overcoming the challenges of non-injected vaccines. The measles patch could be ready as early as two years from now.  And Wired has a nice overview on a couple non-injected methods. Hopefully, we’ll have all sorts of options in the next decade for how we get our vaccines!

Q&A- Why Chickenpox and Rotavirus?

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Anonymous Asks: “Why are vaccines for things like rotavirus and chickenpox on the vaccine schedule when both are common childhood illnesses that are generally not dangerous if treated well (hydration, mainly, for rotavirus)? I just personally struggle with a distrust of the cdc when they recommend vaccines for things that are common and non life threatening. Thanks!” Continued

Q&A: How to Balance Risks and Benefits of Hep B Vaccine

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9131353649_4fc639d9f4_oHailey M. Asks: I am trying to balance the risks versus benefits of the newborn hepatitis B vaccine for my family. I have no problem giving it to my children when they are a little older, but I question doing it at birth when I feel like they have a very minimal chance of coming in contact with hepatitis B. This study seems to suggest that perhaps waiting may be safer? Are you aware of any research that refutes this?

Our Answer: Hi Hailey, thank you for writing to us. We get a lot of questions regarding why the hepatitis B vaccine is given at birth; it’s one many parents wrestle with. Even some of our own staff were initially uncertain about why this vaccine is provided to newborns. I’ll start by addressing your concerns with the study, and then give you some background on why a vaccine for what we typically think of as a sexually transmitted disease is recommended at birth.

This study looks at data concerning maternal recall of newborn hepatitis B vaccine and diagnosis of autism from National Health Information Surveys from 1997­-2002. Maternal recall means that they’re asking women after the fact whether or not their child had the hepatitis B vaccine at birth. These kinds of studies have a very high potential for bias and inaccuracy.

But the more fundamental flaw in this study is that the children surveyed were between 3 and 17 years of age. This means that children were born before and after the introduction of the newborn hepatitis B vaccine. Since autism diagnosis has been rising, mostly from increased awareness and expanded diagnostic criteria, it is expected that this study would show more autism among children vaccinated for hepatitis b. The children that were born before the hepatitis b vaccine was available would have lower rates of autism because it was being diagnosed less frequently.

The study itself also references two other studies, which do not have the same problems as this study and which show no link between giving the hepatitis B vaccine at birth, and autism rates.

I hope that helps to allay some of your concerns about this study; if there’s anything else we can explain about it specifically, please let us know.

As for why the vaccine is given to newborns, the vaccine was originally recommended at birth because there were so many children being born to mothers who had hepatitis B and didn’t know it. Basically only about half of women who had hepatitis B were identified before giving birth. About 16,000 newborns a year were born with a hepatitis B infection, and 90% of newborns who contract the disease become chronic carriers, which puts them at higher risk for cirrhosis and liver cancer. You can see a more detailed explanation of this rationale here.

There were a number of reasons that so many children were born to hepatitis B­ positive mothers who didn’t know it: a) some mothers contracted hepatitis B between testing during prenatal care and giving birth, b) false negatives can occur in testing, c) the wrong testing could have been ordered or the results may have been misinterpreted (hepatitis B testing is a bit more complicated than some other forms of testing), and d) the results could have been miscommunicated between the lab and doctor’s office.

In addition to the possibility of a missed Hepatitis B infection in the mother, the hepatitis B virus can live on surfaces for up to 7 days, including in dried blood. It’s blood­borne, but not just through sexual contact, it can also be transmitted through bites, which happen frequently in daycare or playgroup settings.

Because it can live a week on surfaces, needles or bandaids discarded at city parks, etc. can also be sources of infection. It’s not a common method of transmission, but the risk is not zero either.

Along with this, the Hepatitis B vaccine is one of the safest vaccines with the fewest number of possible side effects (mostly just pain and soreness at the injection site) and no documented serious side effects.

If there is something serious that can happen from the hepatitis B vaccine, it’s so rare that it hasn’t been detected at the level of one dose per several millions of doses. The safety of the vaccine, combined with the possibility of infection at birth or in infancy, is the reason this vaccine in particular is given right at birth. Hepatitis B can be quite serious when contracted at a young age, about a third of kids under 5 who get a hepatitis B infection will become lifetime chronic carriers, and they may never know they were infected ­­ and therefore never know they are carriers.

I hope this helps address your concerns regarding the hepatitis B vaccination, please let us know if you have any other questions.

Further Reading:

A complete explanation from the Immunization Action Coalition of the birth dose of hepatitis B vaccine.

Immunization Action Coalition handout about medical errors related to hepatitis B, showing need for birth dose.

Photo Credit to Joshua Rappeneker. Creative Commons license.

The Risk Assessment Trap

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Photo by Pieter Musterd on Flickr (
Photo by Pieter Musterd on Flickr (

“But what’s the risk that my child will actually catch one of these diseases?”

It’s often one of the first questions parents ask us after we explain the (relatively low) risks of vaccines, and one of the most difficult to answer. It’s very easy to provide data on the outcomes for people who have been infected with a vaccine preventable disease. We can tell you that 1 or 2 in 100 infants who contract pertussis will die, that about 1 in 4 will develop pneumonia. We have these statistics, carefully tracked, for all vaccine preventable diseases, and we can say with a high degree of certainty that there are significantly greater risks to suffering the diseases that we vaccinate for than there are from the vaccines that protect against them. Continued